The invention relates to a threaded drive with a load-bearing nut and a catch nut.
A threaded drive of this kind is known, for instance from German Patent Disclosure DE 103 48 320. FIG. 2 of this reference shows a threaded drive 110 with an axis A, comprising a load-bearing nut and a catch nut 116. The load-bearing nut comprises a main body 114 and a securing body 118. The load-bearing nut and the catch nut are in screwing engagement with the threaded spindle 112, and the catch nut has a greater thread play than the load-bearing nut. This assures that the flow of force can be effected via the load-bearing nut in a first operating state and via the catch nut in a second operating state.
The catch nut can be fixed in a position in which it rests on a bearing face of the load-bearing nut and in which it does not touch the threaded spindle and in particular its thread courses. The first operating state corresponds to the normal operating mode of the threaded drive, in which the load-bearing nut is functioning properly, while in the second operating state, damage has occurred to the load-bearing nut. With the catch nut, the intent is then to prevent a load, which would be lifted by the threaded drive counter to gravity, from dropping.
From German Utility Model DE-GM 19 41 814, a similar threaded drive is known, in which the catch nut is also freely rotatable to the load-bearing nut during operation, particularly in the second operating state. This is intended to assure that damage to the load-bearing nut can be recognized from someone outside from the fact that motion of the threaded drive is not possible, or is now possible only in one direction. An axial mobility of the catch nut relative to the load-bearing nut is also provided.
A disadvantage of this embodiment is that no precautions were taken to prevent the load-bearing nut from touching the threaded spindle. That is especially important whenever a roller body revolution nut is used as the load-bearing nut. In that case, the thread courses of the threaded spindle have a high surface quality, which could be easily destroyed by a catch nut scraping it. The durability of the threaded drive would be impaired as a result.
From German Patent DE 196 25 999 C2, a further threaded drive with a catch nut is known. Here, the catch nut is joined to the load-bearing nut in a manner fixed against relative rotation via a thin web. If the load-bearing nut fails, the web is deformed elastically or plastically in the axial direction, so that an axial motion of the catch nut relative to the load-bearing nut ensues. This motion is detected by a safety switch.
A disadvantage of this embodiment is that the connection between the catch nut and the load-bearing nut can be manufactured and installed only at great effort and expense. For that purpose, the load-bearing nut can be embodied integrally with the catch nut, but this can be accomplished only with difficulty if a hardened roller body revolution nut is employed. If the load-bearing nut and catch nut are embodied separately, on the other hand, a complicated alignment procedure is required to assure that the catch nut will not touch the thread courses of the threaded spindle.